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Comproportionation Reaction and Hindered Rotation of Coordinated Pyridine Rings in an Acetate‐Bridged Tetraplatinum( II ) Cluster with Pyridine‐Based Ligands in the Cluster Plane
Author(s) -
Yamaguchi Tadashi,
Shibata Akira,
Ito Tasuku
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20011217)7:24<5409::aid-chem5409>3.0.co;2-2
Subject(s) - comproportionation , chemistry , pyridine , acetonitrile , ligand (biochemistry) , stereochemistry , crystallography , cluster (spacecraft) , medicinal chemistry , deprotonation , ion , organic chemistry , programming language , biochemistry , receptor , electrode , computer science , electrochemistry
A series of pyridine‐substituted derivatives of octaacetatotetraplatinum( II ), [Pt 4 (CH 3 COO) 8− n (L) 2 n ] n + (L=4‐dimethylaminopyridine (dmap), pyridine (py), 4‐cyanopyridine (cpy); n =1–4) were prepared, and the tetra‐ and octasubstituted forms ( n =2 and 4) were isolated. 1 H NMR spectra showed that this type of cluster undergoes a comproportionation reaction. Reactions between clusters in which n =0 and 2, n =0 and 4, and n =2 and 4 afforded Pt 4 clusters with n =1, 2, and 3, respectively, as a main product in acetonitrile. The dmap‐substituted clusters, trans ‐[Pt 4 (CH 3 COO) 6 (dmap) 4 ](ClO 4 ) 2 ⋅ 3 CH 3 NO 2 ( 3 a (ClO 4 ) 2 ⋅ 3 CH 3 NO 2 ) and [Pt 4 (CH 3 COO) 4 (dmap) 8 ](ClO 4 ) 4 ⋅ 4 H 2 O ( 5 a (ClO 4 ) 4 ⋅ 4 H 2 O), have been structurally characterized. Both 3 a and 5 a have a square‐planar cluster core comprised of four Pt II ions, and all eight out‐of‐plane coordination sites are occupied by acetate ligands in a bridging mode. In 5 a , all of the in‐plane sites are occupied by dmap ligands. In 3 a , four dmap ligands occupy the coordination sites at the two mutually opposite edges of the square planar cluster skeleton, giving a trans tetrasubstituted form of [Pt 4 (CH 3 COO) 8 ] ( 1 ). In octasubstituted 5 a , adjacent dmap ligands are so closely arranged that the Pt−N distances (2.20(3), 2.30(3) Å) are longer than those in tetrasubstituted 3 a (2.13(1), 2.15(1) Å) and related Pt 4 clusters. Furthermore, rotation of the dmap ligand about the Pt−N bond in 5 a was restricted, and the rate constant of the rotation was 4.5 s −1 at 20 °C from dynamic NMR study. Cluster [Pt 4 (CH 3 COO) 5 (dmap) 6 ] 3+ ( 4 a ) also exhibited similar hindered rotation with the rate constants of 2.0 s −1 , 12 s −1 and ≈10 4 s −1 at 20 °C depending on the coordination sites of the dmap ligands in 4 a .